help with old jet boat

i just got a 1973 Kona 21 foot jet boat with a Harden Marine 390 hp OLDS 455 and a jacuzzi jet pump. I bought the boat in Arkansas at 500 ft altitude and am now in Colorado at 4000 ft altitude. How do I tell which jet pump my boat has? It has a weber 4 bbl carb on it also. I took it to lake yesterday for tje first time and it started ok but when i tried to get on plane, the engine sputtered, revved up, sputtered more, and lost rpms never getting on plane. It also felt as if it was very sluggish. My question is twofold- would the change in altitude make this much difference in performance, and is there something I need to check with the pump? The guy I bought the boat from used it every summer weekend last year in Arkansas and said that the pump had a new wear ring the year before...any help?

Re: help with old jet boat

Holley recommends 2 sizes smaller jets (one "size"/2000' ) for operating at higher altitudes

The Weber should be similar. You also probably have an automatic choke that could be sticking.

I would get the carb rebuilt and have the rebuilder put slightly smaller jets in. A local rebuilder will probably know what works there....

Can't help you on the hottub pump...but here's what google found. http://www.glen-l.com/resources/msjetsup.html

Regards,


Rick

Re: help with old jet boat

Thanks for the insight, i will check on the jet size- maybe just get a new carb with more gas sucking ability...

Re: help with old jet boat

Yay another Jet !

Yep drop a couple sizes on the carb jets. and twist her tail.